In many single wafer or batch spray wafer processing systems, an etching solution is lost from the etching solution supply system due to dispensing of the etching solution onto the wafers or substrates in a process chamber. Therefore, refilling of the etching solution supply system is required in order to replace the etching solution. Even if the etching solution is drained from the process chamber and reclaimed by the etching solution supply system, some of the etching solution is lost and the reclaimed etching solution has different physical properties (e.g., temperature and water content) than the etching solution dispensed onto the wafers. A similar situation can occur in wet benches where an etching solution can be lost through drag-out during batch transfers or during either partial or full bath changes.
In order to perform etching processes with good repeatability over the etch rate and etch selectivity between different materials, tight control over the processing conditions is essential. In one example, this includes requirement for tight control over temperature and hydration level of an acidic etching solution in a substrate processing system.